1. Field of the Invention
The present invention relates to centering devices which are mounted on oil well casings, tubings and similar conduit strings for maintaining substantially uniform clearance between such strings and the wellbore.
2. Description of the Prior Art
Centering devices for oil well casings, also known as centralizers, have conventionally consisted of outwardly bowed springs being annularly arranged and attached to axially-spaced collars for placement about an oil well conduit string. A common practice in this field is the welding of a plurality of outwardly bowed springs to collars at the ends of the device. Alternatively, prior devices have been manufactured of uniquely formed collars and springs which can then be assembled without the need for welding. It has been recognized in the prior art that welding adversely affects the physical properties of the springs and also requires substantial investment in specialized fixtures, jigs and welding equipment to complete the manufacture of these prior centering devices. It has also been found that this method of manufacture and assembly results in a centering device which is costly to transport and store due to the low weight per volume ratio inherent to the welded type centering device. Accordingly, it has been recognized that the welding of centralizers should be avoided as described in Canadian Pat. Nos. 800,828, and 712,423. These patents describe a centralizer device which can be shipped within confined spaces and allow for assembly at the point of use. However, the centralizer device described in Canadian Pat. No. 712,423 utilizes a spot welding process in the assembly of the inner sleeve and outer collar section and furthermore requires the use of substantial effort and proper tools for disassembly. Furthermore, the centralizer of Canadian Pat. No. 712,423 has the inherent feature that bending and torsional stresses are applied by a portion of the outwardly bowed springs after the centralizer has been assembled. Canadian Pat. No. 800,828 describes a centralizer which, unlike the centralizer described in Canadian Pat. 712,423, requires that a portion of the centralizer collar, described as the tongue therein, is to be bent in order to assemble the spring to the centralizer collar. The required force to bend the tongue during the assembly procedure is considerable and as a result of this force generally being applied to the tongue by the use of a hammer or other such object being used by a person, this applied force is generally inconsistent and uncontrollable, thus resulting in possible damage of the centralizer collar. With such a centralizer collar being damaged, installation of the assembled centralizer to the conduit string can be hampered.
The present centralizer device improves upon prior non-welded centralizers by not requiring deformation or bending of its elements during assembly of the device. Accordingly, all technical skills and quality control required in the forming of the centralizer elements is maintained within the manufacturing facility.